1. Field of the Invention
The present invention relates generally to removing color noise in an image signal, and more particularly, to performing different levels of low pass filtering on the image signal depending on whether an object pixel is in an even region, an intermediate region, or an edge region.
2. Background of the Invention
An image signal for an image is generated by photographing an object using a photographing device including an image sensor. The image signal is processed such as by being modulated and then transmitted to a display device through a wired or wireless channel. The display device restores the received image signal through further signal processing such as by demodulation and displays an image corresponding to the restored image signal.
FIG. 1 is a block diagram of an image signal processor (ISP) for processing an image signal generated by an image sensor 102. Referring to FIG. 1, the image signal processor includes a line memory controller 104, an interpolator 106, and a converter 108.
The image sensor 102 generates an image signal in a predetermined format from light Lin corresponding to an image. The image sensor 102 of FIG. 1 generates a Bayer color pattern signal having the Bayer color pattern format. The Bayer color pattern format is known to one of ordinary skill in the art. The line memory controller 104 aligns the Bayer pattern color signal from the image sensor 102 line by line to generate an M-line Bayer pattern color signal.
The interpolator 106 interpolates the M-line Bayer pattern color signal using correlation of signals corresponding to respective pixels to generate color component RGB (red, green, and blue) signals for each pixel. The converter 108 converts the RGB signals into final Y (luminance) and C (chrominance) signals. The Y and C signals are transmitted to a display device such as a TV set through a wired or wireless channel.
The image signal from the image sensor 102 may include color noise that may be mixed with an ideal image signal during image signal processing in FIG. 1. Various image signal processing techniques have been proposed to remove the color noise. However, conventional image signal processing techniques use uniform low pass filtering to remove the color noise without considering whether an image area is for an even region or an edge region.
When the image area is for an even region, the image signal has small variation in such an image area. When the image area is for an edge region, the image signal has large variation in such an image area. While low pass filtering for the even region removes the color noise, low pass filtering for the edge region may deteriorate the definition of the image.